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Propagation at HF: What can we learn using digital modes WSPR and FST4W?

Gwyn Griffiths, G3ZIL

This presentation is a story of learning-as-I-went-along with the Weak Signal Propagation Reporter (WSPR) mode within the WSJT-X digital communications package. It begins with building a simple, but successful, 7 MHz WSPR transceiver.

My next WSPR receiver went to the Arctic on an icebreaker, receiving three spots in eight days. Why? We’ll delve into how the ionosphere affects narrowband signals like WSPR. We’ll see why frequency spread, as in auroral flutter, is important. How do we measure it? Enter the FST4W mode. Frequency spread is not just a useful measure on auroral paths. I’ll show how to identify one-hop and multi-hop signals, where the path was likely a chordal hop or a Pedersen ray, or when my 14 MHz signal from Southampton reached London via two ionospheric refractions and the Mediterranean.

To convince you that’s quite likely we’ll look at ray trace model predictions and results of a rotating-beam experiment. To close, I’ll use these tools to show effects on the ionosphere of the 14 October 2023 annular eclipse over the USA.

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